Just think of this, in order to make a movie you need, first and most important of all, an IDEA, then you choose the tools that will help you achieve the results that you want. Nowadays, 3D tools are all about workflow and time saving features, but they all can achieve similar results, and I’m including Blender in here. It’s just a matter of time, money and the ability to make your way around problems.
Then you need characters (Blender has amazing features for modeling, rigging, texturing and animating character), and you need lighting (there are lots of things you can do without the need of having Renderman or MentalRay, it all depends on how good you are for solving poblems and finding tricky but effective solutions.). You must remember that in 3D animation everything is about faking things, so you don’t really need to have a super realistic huge rendering engine. Take a look at Shrek 1, the guys from Dreamworks couldn’t afford using indirect lighting, so they faked it all with precise direct lighting design. Just as you would do it inside of Blender.
And finally, you need rendering power (if you have the money), or a lot of time to spend rendering with just one computer (if you don’t have money).
That’s my opinion. The Pixar guys have a lot of money, and they have strict deadlines, so they rely on rendering power. If you are a Blender User, like the Plumiferos guys, you don’t have money, you don’t have much rendering power, so you have to think how to solve things the best way possible but spending the less amount of resources that you can.
I’m not comparing Plumiferos movie quality with Pixar, there’s a BIG $$$$$$$ difference, but take a look at Elephant Dreams image quality, or the new Peach projects Fur renders, and you’ll see that Blender is technologically capable of achieving Pixar quality level results. You just need money, workflow intelligence and time.